A method and an apparatus for ultrasonic staking a first part having a fastening portion to a second part having an opening corresponding to the fastening portion. The method comprises aligning the fastening portion of the first part with the corresponding opening in the second part, inserting a head of the fastening portion through the corresponding opening, and causing a horn of an ultrasonic staking stack to contact the head, apply ultrasonic energy oscillating at a frequency between 45 kHz and 75 kHz, and move along an axis of the fastening portion as the head melts to form a stake. The stake can include a melt-form that joins the first part and the second part to each other, and the fastening portion can have a geometry or a size disposed to flapping.